As I’ve mentioned a few times before, Atebits’ Tweetie for Mac is my favorite desktop Twitter client. (And many people also enjoy the $2.99 Tweetie iPhone application from the same developer.)

What has developer Loren Brichter been doing in the wake of the applications’ popularity? Writing Tweetie 2.0, of course! Tweetie 2 for iPhone is nearing it’s release, and Tweetie 2 for Mac is in the works as well.

At the same time I knew that Tweetie 1.x could only go so far. Like the original Mac OS, it blended an intuitiveness with a well rounded set of features. But the “core” needed to be replaced. Not one to rest on my laurels, I started Project Bigbird, which was a new Twitter “core” meant to last.

What is hoped to be the final beta of the new Tweetie for iPhone has been sent to Apple for approval. It includes the “Project Bigbird” core that has been built into Tweetie for Mac since its beginning. It only works on OS 3.0+, as it has plenty of new features, some of which make use of APIs added in OS 3.x.

…there is also a fantastic offline mode. You can favorite, follow, block, add to Instapaper and more all while offline. Next time you connect, all of those actions will be synced back up.

You also get threaded @reply conversations, just like the desktop app, full landscape mode, gesture shortcuts, support for Project Retweet, and a ton of other neat things.

That’s just the iPhone version of Tweetie 2, which will cost $2.99 for new and existing users. Tweetie 2 for Mac will be a free upgrade for existing users, though I haven’t heard of any details or a release timeline yet.